This invention relates to internally lubricated, ball-recirculating ball screw and nut assemblies and is concerned with the actuator, the method of making the actuator, and the method of lubricating the actuator.
The difficulty of providing lubrication to ball screw and nut assemblies in a manner to provide a continuous and consistent lubrication of the moving parts is well appreciated in the prior art. Such lubrication is particularly critical in industries such as the aircraft industry and others where poor and inadequate maintenance performed in the field might have a serious life-endangering consequence.
Various prior art structures have been suggested for internally lubricating linear actuators and some have provided a lubricant carrier in direct engagement with the screw in the manner of U.S. Pat. No. 6,125,968, which I incorporate herein by reference.
Other suggestions have involved the use of a molded lubricant-containing polymer member which is in direct contact with the recirculating balls traveling in the raceway of the ball screw and nut assembly, and I refer particularly to U.S. Pat. No. 6,023,991, which I also incorporate herein by reference.
In both of these assemblies the lubricant containing member is in direct engagement with moving parts of the assembly and a constant wear inevitably occurs which ultimately affects proper distribution of the lubricant.
The present invention is directed to a linear actuator wherein an axially extending portion of the nut has a series of ball return passages opening to the screw groove which span different turns of the screw groove. Ports are provided which extend to communicate with the ball return passages, and a lubricant distributor supplies lubricant to the ports.
In a preferred embodiment of the invention, the distributor may comprise a wicking lubricant carrier pad extending axially along the nut to span the ports and the pad may be in contact with a lubricant reservoir in the form of a foam pad housed in a reservoir cap carried on the nut.
One of the prime objects of the present invention is to provide a constant supply of clean oil to ports which meter separate flows at a constant rate through to the ball return passages.
Still another object of the invention is to, in this manner, avoid any contact of the lubricant carrier with moving parts.
Another object of the invention is to effectively lubricate the ball screw and nut assembly for extended periods to thereby increase lubrication service intervals.
Still another object of the invention is to provide a simpler and more economically manufactured linear actuator which eliminates a number of the parts needed to perform prior lubrication functions, and provides a product with a much more compact and streamlined footprint.
Still another object of the invention is to provide a linear actuator with a more durable and robust internal lubrication system using a minimum number of components which can be readily retrofitted to existing designs.
Still another object of the invention is to provide a linear actuator which has increased life expectancy by virtue of the continuous metered lubrication, and which is easily serviced in the field without dismantling it from the system being actuated.
Still a further object is to provide an internally lubricated ball screw and nut assembly which is tunable to the lubricant used.
Other objects and advantages of the invention will become apparent with reference to the accompanying drawings and the accompanying descriptive matter.